2. Field of the Invention
The present invention relates to an apparatus for determining conditions of various kinds of sheets such as securities.
2. Description of the Related Art
As shown in the U.S. Pat. No. 4,374,463 (Feb. 22, 1983), a conventional apparatus automatically classifies various kinds of sheets to be discriminated, such as securities, into three groups: a first group of sheets which have not been substantially stained, a second group of sheets which have been substantially stained and a third group of sheets which have been forged for unjust purposes. One example of the third group of sheets may be a sheet S which has been reproduced as if one sheet by joining intentionally cut pieces of two different sheets S1 and S2 with an adhesive tape T applied, as shown in FIG. 2.
On the conventional apparatus for discriminating sheets, a thickness of a sheet to be discriminated is measured over its whole surface and a portion of the sheet thicker than the original thickness is detected through this measurement as a portion on which an adhesive tape is applied. A sheet with adhesive tape applied from one end to the other of the sheet was discriminated to be the third group of sheets.
In the conventional apparatus for discriminating sheets such as described above, those sheets with adhesive tape applied from one end to the other Of the sheet are all classified to be in the third group of sheets. Therefore, there was a problem that sheets which should have been classified in the second group of sheets were instead classified in the third group of sheets. As a result, a sheet that was originally one sheet but was cut completely into two separate pieces and then restored to one sheet by mending using an adhesive tape and which should have been classified in the second group of sheets, was classified in the third group.